UL Et .Im 
AMERICAN NATURALIST. 
Vol. IV.—JUNE, 1870. — No. 4. 
coc Gu (RO ER > 
THE | SURFACE GEOLOGY OF THE BASIN OF THE 
GREAT LAKES AND THE VALLEY OF THE 
MISSISSIPPI. 
BY PROFESSOR J. S. NEWBERRY. 
THE area bounded on the north by the Eozoic highlands 
of Canada, on the east by the Adirondacks and the. Allegha- 
nies, and on the west by the Rocky Mountains, though now, 
and apparently always, drained by two systems of water- 
courses, may be properly considered as one topographical 
district ; since much of the water-shed which separates its 
two river systems is of insignificant height, is composed of 
unconsolidated “Drift” materials, has shifted its position 
hundreds of miles, as the water level in the great lakes has 
varied, and was for a long interval submerged beneath a 
water connection uniting both drainage systems in one. 
In this great hydrographic basin the surface geology pre- 
sents a series of phenomena of which the details, carefully 
studied in but few localities, still offer an interesting and 
almost inexhaustible subject of investigation, but which, as 
it seems to me, are already sufficiently well known to enable 
us to write at least the generalities of the history which they 
record, 
The most important facts which the study of the “Drift 
! the r 1870, by the PEABODY ACADEMY OP 
Entered according to Act of Co in yea m HA - ing 
SCIENCE, in the Clerk's Office of the District Court of the 
AMER. NATURALIST, VOL. IV. 25 
